There is no Olive GIBBS, or Olive AUSTIN, in the online death indexes - BDM Online - Historical Records (
https://www.bdmhistoricalrecords.dia.govt.nz/Home/) - fitting your description. If she had died in New Zealand, I'd expect to find her there.
Likewise, I don't see her listed in the phone book (
http://yellow.co.nz/whitepages/), but there are people named GIBBS living in Whangarei and one or more may be related to her and be able to tell you how to get in touch.
Hope this helps. :-)
Kind Regards,
Wendy